<!DOCTYPE html>
<html lang="en">

<head>
    <meta charset="UTF-8">
    <meta name="viewport" content="width=device-width, initial-scale=1.0">
    <meta http-equiv="X-UA-Compatible" content="ie=edge">
    <title>domain</title>
</head>

<body style="border:1px solid red">
    b页面
    <script>
        document.domain = "zbc.com"
        var b = "b页面的数据"
        alert(window.parent.a)
    </script>
</body>

</html>